Variable interatrial conduction illustrated in a hypertrophic cardiomyopathy population

Abstract

Background: Patients with hypertrophic cardiomyopathy (HCM) have a high incidence of atrial fibrillation. They also have a longer P-wave duration than healthy controls, indicating conduction alterations. Previous studies have demonstrated orthogonal P-wave morphology alterations in patients with paroxysmal atrial fibrillation. In the present study, the P-wave morphology of patients with HCM was compared with that of matched controls in order to explore the nature of the atrial conduction alterations.

Methods and results: A total of 65 patients (45 men, mean age 49 +/- 15) with HCM were included. The control population (n = 65) was age and gender matched (45 men, mean age 49 +/- 15). Five minutes of 12-lead ECG was recorded. The data were subsequently transformed to orthogonal lead data, and unfiltered signal-averaged P-wave analysis was performed. The P-wave duration was longer in the HCM patients compared to the controls (149 +/- 22 vs 130 +/- 16 ms, P < 0.0001). Examination of the P-wave morphology demonstrated changes in conduction patterns compatible with interatrial conduction block of varying severity in both groups, but a higher degree of interatrial block seen in the HCM population. These changes were most prominent in the Leads Y and Z.

Conclusion: The present study suggests that the longer P-wave duration observed in HCM patients may be explained by a higher prevalence of block in one or more of the interatrial conduction routes.

Figure 1

Schematic illustration of the signal‐averaged P‐wave morphologies. The derived parameters are indicated with dashed lines. Lead X: X_max location (A) and amplitude (B); Lead Y: Y_max location (C) and amplitude (D); Lead Z: Z_min location (E) and amplitude (F), Z_zero location (G), Z_max location (H) and amplitude (I); Spatial magnitude (SM); location of the maximum peak (SM₁) (J) and the negative extreme (Nadir) (L). If a second peak was identified (SM₂) (K), its location and distance to SM₁ were calculated.

Figure 2

Typical examples of Type 1 P‐wave morphology (A), and Type 2 P‐wave morphology (B). Type 3 P‐wave morphology (C) was identified in 11 patients (10 HCM patients and 1 control subject). The pattern is compatible with Bachmann's bundle block. ²³ Two patients from the HCM population were excluded from subsequent analysis because of P‐wave morphology noncompatible with sinus rhythm (i.e., predominantly negative Lead Y).

Figure 3

The presence of discrete pathways was further explored using the relative position of the zero crossing in Lead Z (Z_zero/P_dur). As seen in the histogram, the parameter is not normally distributed (P < 0.01, Shapiro‐Wilk W test) with two different peaks visible. The two peaks represent Type 2 or 3 and Type 1 morphologies, respectively.